Modified Y-type molecular sieve, catalytic cracking catalyst comprising the same, their preparation and application thereof

Abstract

A modified Y-type molecular sieve has a rare earth content of about 4-11% by weight on the basis of rare earth oxide, a sodium content of no more than about 0.7% by weight on the basis of sodium oxide, a zinc content of about 0.5-5% by weight on the basis of zinc oxide, a phosphorus content of about 0.05-10% by weight on the basis of phosphorus pentoxide, a framework silica-alumina ratio of about 7-14 calculated on the basis of SiO2/Al2O3 molar ratio, a percentage of non-framework aluminum content to the total aluminum content of no more than about 20%, and a percentage of the pore volume of secondary pores having a pore size of 2-100 nm to the total pore volume of about 15-30%. The modified Y-type molecular sieve has a high crystallinity, a structure comprising secondary pores, and a high thermal and hydrothermal stability.

The invention claimed is: 
     
       1. A modified Y-type molecular sieve, having a rare earth content of about 4% to about 11% by weight on the basis of rare earth oxide, a sodium content of no more than about 0.7% by weight on the basis of sodium oxide, a zinc content of about 0.5% to about 5% by weight on the basis of zinc oxide, and a phosphorus content of about 0.05% to about 10% by weight on the basis of phosphorus pentoxide, based on the weight of the modified Y-type molecular sieve on a dry basis; a framework silica-alumina ratio of about 7 to about 14 calculated on the basis of SiO 2 /Al 2 O 3  molar ratio, a percentage of non-framework aluminum content to the total aluminum content of no more than about 20%, and a percentage of the pore volume of secondary pores having a pore size of 2-100 nm to the total pore volume of about 15% to about 30%. 
     
     
       2. The modified Y-type molecular sieve according to  claim 1 , wherein the modified Y-type molecular sieve has one or more of the following characteristics:
 a total pore volume of the modified Y-type molecular sieve of about 0.33 mL/g to about 0.39 mL/g; 
 a lattice constant of the modified Y-type molecular sieve of about 2.440 nm to about 2.455 nm; 
 a percentage of non-framework aluminum content to the total aluminum content of the modified Y-type molecular sieve of about 13% to about 19%; 
 a percentage of the pore volume of secondary pores having a pore size of 2-100 nm to the total pore volume of the modified Y-type molecular sieve of about 20% to about 30%; 
 a ratio of B acid to L acid in the strong acid content of the modified Y-type molecular sieve of no less than about 3.50, as determined by pyridine adsorption infrared spectroscopy at 350° C.; 
 a lattice collapse temperature of the modified Y-type molecular sieve of not lower than about 1050° C.; 
 a relative crystallinity of the modified Y-type molecular sieve of no less than about 60%; and/or 
 a relative crystallinity retention of the modified Y-type molecular sieve of about 35% or more after being aged at 800° C. under atmospheric pressure in a 100 vol % steam atmosphere for 17 hours. 
 
     
     
       3. The modified Y-type molecular sieve according to  claim 1 , wherein the modified Y-type molecular sieve has a rare earth content of about 4.5% to about 10% by weight, a sodium content of about 0.4% to about 0.6% by weight, a phosphorus content of about 0.1% to about 6% by weight, based on the weight of the modified Y-type molecular sieve on a dry basis; a lattice constant of about 2.440 nm to about 2.453 nm, and a framework silica-alumina ratio of about 8.5 to about 12.6. 
     
     
       4. A method for the preparation of a modified Y-type molecular sieve according to  claim 1 , comprising the steps of:
 (1) contacting a NaY molecular sieve with a rare earth salt solution for ion-exchange reaction, to obtain an ion-exchanged molecular sieve; 
 (2) subjecting the ion-exchanged molecular sieve to a hydrothermal ultra-stabilization treatment, to obtain a hydrothermally ultra-stabilized molecular sieve; 
 (3) subjecting the hydrothermally ultra-stabilized molecular sieve to phosphorus modification by contacting with a phosphorus compound, to obtain a phosphorus-modified molecular sieve; 
 (4) subjecting the phosphorus-modified molecular sieve to a gas phase ultra-stabilization treatment by contacting and reacting with gaseous SiCl 4 , to obtain a gas phase ultra-stabilized molecular sieve; and 
 (5) impregnating the gas phase ultra-stabilized molecular sieve with a zinc salt solution, to obtain the modified Y-type molecular sieve. 
 
     
     
       5. The method according to  claim 4 , wherein the step (1) further comprises contacting a NaY molecular sieve with a rare earth salt in an aqueous solution for ion-exchange reaction, wherein the ion-exchange reaction is conducted under the following conditions:
 a reaction temperature of about 15° C. to about 95° C., a reaction time of about 30 min to about 120 minutes, and a mass ratio of the NaY molecular sieve, the rare earth salt, and water of about 1: (0.01-0.18): (5-15), wherein the mass of the NaY molecular sieve is calculated on a dry basis, and the mass of the rare earth salt is calculated on the basis of rare earth oxide. 
 
     
     
       6. The method according to  claim 4 , wherein the hydrothermal ultra-stabilization treatment of the step (2) is carried out by roasting at a temperature of about 350° C. to about 480° C. in an atmosphere comprising about 30% to about 90% by volume of steam for about 4.5 h to about 7 h. 
     
     
       7. The method according to  claim 4 , wherein in the step (3), the phosphorus modification is conducted at a temperature of about 15° C. to about 100° C. for a period of about 10 min to about 100 min;
 preferably, the phosphorus compound used for the phosphorus modification is one or more selected from the group consisting of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. 
 
     
     
       8. The method according to  claim 4 , wherein in the step (4), the reaction temperature is about 200° C. to about 650° C., the reaction time is about 10 minutes to about 5 hours, and the mass ratio of SiCl 4  to the phosphorus-modified molecular sieve is about (0.1-0.7):1, wherein the mass of the phosphorus-modified molecular sieve is calculated on a dry basis. 
     
     
       9. The method according to  claim 4 , wherein the step (5) further comprises subjecting the impregnated molecular sieve to calcination, wherein the impregnation temperature is about 10° C. to about 60° C., the calcination temperature is about 350° C. to about 600° C., and the calcination time is about 1 hour to about 4 hours. 
     
     
       10. A catalytic cracking catalyst, comprising, based on the weight of the catalyst on a dry basis, about 10% to about 50% by weight of a modified Y-type molecular sieve, a binder, and clay; wherein the modified Y-type molecular sieve is a modified Y-type molecular sieve according to  claim 1 . 
     
     
       11. The catalytic cracking catalyst according to  claim 10 , wherein the catalyst comprises about 10% to about 50% by weight of the modified Y-type molecular sieve, about 10% to about 40% by weight of a binder and about 10% to about 80% by weight of clay, based on the weight of the catalyst on a dry basis. 
     
     
       12. The catalytic cracking catalyst according to  claim 10 , wherein the clay is selected from the group consisting of kaolin, hydrated halloysite, montmorillonite, diatomaceous earth, halloysite, saponite, rector, sepiolite, attapulgite, hydrotalcite, bentonite, and any combination thereof. 
     
     
       13. The catalytic cracking catalyst according to  claim 10 , wherein the binder is an alumina binder selected from the group consisting of alumina, hydrated alumina, aluminum sol, and any combination thereof, and the content of the binder is calculated on the basis of alumina. 
     
     
       14. A method for catalytic cracking of hydrocarbon, comprising contacting the modified Y-type molecular sieve according to  claim 1  with a hydrocarbon feedstock under catalytic cracking conditions. 
     
     
       15. The method according to  claim 14 , wherein the hydrocarbon feedstock is a hydrogenated light cycle oil, and the catalytic cracking conditions include: a reaction temperature of about 500° C. to about 610° C., a weight hourly space velocity of about 2 h −1  to about 16 h −1 , and a catalyst-to-oil weight ratio of about 3 to about 10.